These are but a few examples of how the Chromotrops (one of the most interesting series of dye-stuffs at the service of the dyer) may be used to dye blacks. They of themselves dye brilliant reds, from bright scarlet (2 R), crimson (6 B), and purple (8 B and 10 B), to maroon and clarets (S and S B). These being turned black on being chromed, give various shades--blue blacks, violet blacks, and jet blacks, which have the merit of being fast to acids, strong milling, and light in a great degree. The blue and violet blacks may be converted to jet (p. 095) shades by adding to the dye-bath some yellow dye-stuff, such as Azo Yellow, Alizarine Yellow, or Gambine Yellow, which will resist the action of the bichrome in the developing bath. Chromotrop blacks while so very fast have the disadvantage of being expensive, but by combining them with logwood it is possible to obtain blacks that have a great degree of resistance to light, acids and milling. They are in this respect much superior to pure logwood blacks, while the cost is not prohibitive. The following recipe will serve as an example of how these two dye-stuffs may be combined:-- _Jet Black_.--Make a bath with 2 lb. Chromotrop S, 15 lb. Glauber's salt, and 5 lb. hydrochloric acid. Work in this bath for one hour, then add 2-1/2 lb. bichromate of potash, and work again for half an hour, at the boil. Lift, rinse and dye in a new bath containing 25 lb. logwood, 1 lb. fustic extract and 1/4 lb. sulphuric acid, working at the boil for an hour. _Violet Black on Wool_.--Dye the wool in the Chromotrop bath, and develop as in the last recipe. The final dye-bath is made with 6 lb. logwood, 8 oz. Patent Blue B, and 4 lb. sulphuric acid. By using logwood alone blue blacks can be dyed, by increasing the proportion of fustic a greener tone can be obtained, while by the use of a larger proportion of Chromotrop a redder tone of black is the result. _Jet Black_.--Make the dye-bath with 20 lb. Glauber's salt, and 6 lb. Nyanza Black; when obtained is a good one and of solid appearance. Alkalies turn it red, but it is fast to dilute acid and soaping. _Black_.--Prepare the dye-bath with 10 lb. Glauber's salt, 5 lb. oxalate of ammonia, 5 lb. acetic acid and 6 lb. Anthracene Chrome Black F. Work at the boil for three-quarters of an hour, or until (p. 096) the bath is exhausted of dye-stuff, then add 1-1/2 lb. bichromate of potash and 2 lb. hydrochloric acid to the same bath and work for half an hour longer. The Anthracene Chrome Blacks, of which there are three brands, F, 5 B and F E, are excellent dyes, producing very fine blacks, and owing to the slowness of dyeing and great penetrative properties are very suitable for dyeing hat felts and other closely woven fabrics. The 5 B dyes more bluish shades than the F, while the F E brand gives full black. By combining these with Anthracene Yellow B N, Anthracene Acid Brown G, or other similar dyes, jet blacks can be got as per the following recipe:--